Damped actuator and valve assembly for an electronically-controlled injector

ABSTRACT

An actuator and valve assembly for an electronically-controlled injector is disclosed which comprises an electrically-energizable actuator assembly and a device for communicating, collecting and draining damping fluid with respect to at least one cavity of the actuator assembly. If too much damping fluid remains in the actuator assembly after engine shutdown, that damping fluid may cool off and cause slow response of the actuator and valve assembly during cold engine starting. The end result is that quick starting and/or operation of the engine may be hindered, particularly under cold engine conditions. The communicating, collecting and draining means permits at least a portion of the hot damping fluid to automatically drain from the cavity after the engine has been shutdown.

This is a continuation under 37 C.F.R. Section 1.62 of application Ser.No. 08/127,727, filed on Sep. 28, 1993, now abandoned, which is acontinuation under 37 C.F.R. Section 1.53 of application Ser. No.07/776,512, filed on Oct. 11, 1991, now abandoned.

TECHNICAL FIELD

The present invention relates generally to fuel injectors and, moreparticularly to electronically-controlled unit injectors.

BACKGROUND ART

Examples of electronically-controlled unit injectors for an engine areshown in U.S. Pat. No. 3,689,205 issued to Links on Sep. 5, 1972 andU.S. Pat. No. 4,392,612 issued to Deckard et al. on Jul. 12, 1983. InLinks the fuel pumping plunger of the unit injector is hydraulicallyactuated whereas in Deckard et al. the fuel pumping plunger ismechanically actuated. In both of these electronically-controlled unitinjectors, a solenoid assembly is provided which moves a poppet valvethat controls actuating fluid or fuel pressure in the unit injector inorder to control fuel injection delivery.

In the above electronically-controlled unit injectors, the motion of anarmature of the solenoid assembly is hydraulically damped in order tohelp prevent the poppet valve from rebounding after it has contacted aseat or stop. In Deckard et al., the armature has a plurality ofpassages which extend through the armature for the passage of fuelduring movement of the armature toward the opposed working face of anassociated pole piece or stator. In Links, a channel is providedexternal to the armature which communicates with a pair of chamberslocated adjacent opposite end portions of the armature.

However, after the engine is stopped, an excessive amount of suchdamping fluid might remain in the solenoid assembly. This remainingfluid may then become more viscous as the engine cools off. Such viscousfluid may then cause slow response of the solenoid assembly and poppetvalve during cold engine starting. Slow response of the solenoidassembly and poppet valve diminishes the fuel injection deliverycapability and injection timing accuracy of the unit injector. The endresult is that too much damping fluid in the solenoid assembly mayhinder quick starting and/or operation of the engine, particularly undercold engine conditions.

The present invention is directed to overcoming one or more of theproblems as set forth above.

DISCLOSURE OF THE INVENTION

In one aspect of the present invention an actuator and valve assemblyfor an electronically-controlled unit injector is disclosed. Theactuator and valve assembly comprises an electrically-energizableactuator assembly including a movable member defining a cavity and meansfor selectively communicating damping fluid with respect to the cavityonly when the viscosity of the damping fluid is below a selected value.

The selective communicating means not only helps minimize any adversepumping effect that the movable member would normally impart on theactuating fluid contained in the cavity but it also permits dampingfluid that has been communicated to the cavity to drain back to a sumpwithout hydraulically locking the position of the movable member.Furthermore, the communicating means also permits at least a portion ofthe hot damping fluid to drain from the cavity so that the damping fluidcannot remain there, cool off, and significantly hinder quick startingand/or operation of the engine, particularly under cold engineconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic general schematic view of ahydraulically-actuated electronically-controlled unit injector fuelsystem of the present invention, including both an actuating fluidcircuit and a fuel injection circuit, for an internal combustion enginehaving a plurality of unit injectors;

FIG. 2 is a diagrammatic partial cross-sectional view of one embodimentof a unit injector of FIG. 1 as installed in an exemplary internalcombustion engine;

FIG. 3 is a diagrammatic isolated enlarged cross-sectional view of theunit injector shown in FIG. 2;

FIG. 4 is a diagrammatic enlarged partial view of an upper portion ofthe unit injector shown in FIG. 3;

FIG. 5 is a diagrammatic enlarged partial view of a lower portion of theunit injector shown in FIG. 3;

FIG. 6 is a diagrammatic exploded isometric view of a first portion ofcomponents shown in the unit injector of FIG. 3;

FIG. 7 is a diagrammatic exploded isometric view of a second portion ofcomponents shown in the unit injector of FIG. 3;

FIG. 8 is a diagrammatic exploded isometric view of a third portion ofcomponents shown in the unit injector of FIG. 3;

FIG. 9 is a diagrammatic exploded isometric view of a fourth portion ofcomponents shown in the unit injector of FIG. 3;

FIG. 10 is a diagrammatic exploded isometric view of a fifth portion ofcomponents shown in the unit injector of FIG. 3;

FIG. 11 is a diagrammatic exploded isometric view of a sixth portion ofcomponents shown in the unit injector of FIG. 3;

FIG. 12 is a diagrammatic detailed schematic view of the hydraulicallyactuating fluid and damping fluid supplying means generally shown inFIG. 1; and

FIG. 13 is a diagrammatic detailed schematic view of the fuel supplyingmeans generally shown in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1-13, wherein the same reference numerals designatethe same elements or features throughout all of the FIGS. 1-13, a firstembodiment of a hydraulically-actuated electronically-controlled unitinjector fuel system 10, hereinafter referred to as a HEUI fuelinjection system. The exemplary HEUI fuel injection system 10 is shownin FIGS. 1, 2, 12, and 13 as adapted for a diesel-cycle direct-injectioninternal combustion combustion engine 12. While a vee-type eightcylinder engine is illustrated in FIGS. 1, 12 and 13 and describedherein, it should be understood that the invention is also applicable toother types of engines, such as in-line cylinder engines and rotaryengines, and that the engine may contain fewer or more than eightcylinders or combustion chambers. The exemplary engine 12, onlypartially shown in FIG. 2, has a pair of cylinder heads 14. Eachcylinder head 14 has one or more (for example, four) unit injector bores16.

Referring to FIGS. 1 and 2, the HEUI fuel injection system 10 includesone or more hydraulically-actuated electronically-controlled unitinjectors 18 adapted to be positioned in a respective unit injector bore16, means or device 20 for supplying hydraulically actuating fluid anddamping fluid to each unit injector 18, means or device 22 for supplyingfuel to each unit injector 18, and means or device 24 for electronicallycontrolling the HEUI fuel system 10.

Referring to FIG. 3, each unit injector 18 has a longitudinal axis 26and includes an actuator and valve assembly 28, a body assembly 30, abarrel assembly 32, and a nozzle and tip assembly 34. The longitudinalaxis 26 defines a selected angle A with respect to the axis of theengine combustion chamber.

The actuator and valve assembly 28 is provided as a means or device forselectively communicating either relatively-high-pressure actuatingfluid or relatively-low-pressure damping fluid to each unit injector 18in response to receiving an electronic control signal S₁₀ shown inFIG. 1. Referring to FIGS. 3, 4, 6 and 8, the actuator and valveassembly 28 includes an actuator 36, preferably in the form of asolenoid assembly, and a valve 38, preferably in the form of a poppetvalve. The solenoid assembly 36 includes a fixed stator assembly 40 anda movable armature 42.

As shown in FIGS. 3 and 6, the stator assembly 40 includes a one or morefirst fasteners 44, a stator 46, and an electrical connector 48.Although not shown, the stator 46 may, for example, include a stack ofindividual E-frames and an electrical wire which is wound around theE-frames in a conventional manner.

As shown in FIGS. 4 and 6, the armature 42 has a pair ofoppositely-facing planar first and second surfaces 52,54 and a means ordevice 56 for communicating, collecting and draining damping fluid withrespect to expandable and contractible cavities of the solenoid assembly36. As shown in FIG. 4, the first surface 52 of the armature 42 isspaced from the stator 46 so that the armature 42 and stator 46collectively define an upper armature cavity 57 or gap therebetween.

Preferably, the communicating, collecting and draining means 56 includesone or more passages 58 which longitudinally extend between the firstand second surfaces 52,54. For example, as shown in the FIGS. 4 and 6,the passages 58 are provided in the form of a pair of circular holes.Moreover, the communicating, collecting and draining means 56 furtherincludes one or more elongated collection grooves 60 formed in the firstsurface 52 of the armature 42 which directly faces the stator 46. Eachcollection groove 60 laterally extends across the width of the firstsurface 52 and intersects or communicates with a respective passage 58.For example, as shown in FIGS. 4 and 6, a pair of mutually parallelcollection grooves 60 are provided for collecting damping fluid whichhas been communicated to and has accumulated in the upper armaturecavity 57. In an alternative embodiment, passages of elongated orelliptical cross-section may be substituted for the passages 58 ofcircular cross-section. In another alternative embodiment, thecollection grooves 60 may be similarly formed in the portion of thestator 46 facing the first surface 52 of the armature 42 and alsocommunicate with the passages 58 of the armature 42. In other words, thecollection grooves 60 may be formed in one of or both the stator 46 andthe armature 42. The size and position of each passage 58 and collectiongroove 60 is carefully selected to ensure that it has a large enoughvolume to adequately communicate, collect and drain damping fluid withrespect to cavities of the solenoid assembly 36, including the upperarmature cavity 57, but also small enough to maximize the amount of fluxpaths in the stator 46 and armature 42 which are necessary for adequatemagnetic performance of the solenoid assembly 36.

As shown in FIG. 4, a closely-controlled axial clearance or gap C₁ (forexample, about 0.377 millimeters or 0.0148 inches) is defined betweenthe armature 42 and the stator 46 when the armature 42 is in itselectrically deenergized position. The clearance C₁ defines part of theupper armature cavity 57 and helps determine the amount of dampingimparted to the movable armature 42 by the damping fluid which isperiodically displaced from the clearance C₁. The clearance C₁ alsohelps determine the amount of magnetic force imparted by the stator 46to the armature 42 when the solenoid assembly 36 is electricallyenergized.

As shown in FIG. 3, as well as FIGS. 2, 4, 6 and 7, the body assembly 30includes one or more second fasteners 62, an annular armature spacer 64,one or more third fasteners 66, an adapter o-ring seal 68, a poppetadapter 70, an annular unit injector clamp 72, a poppet shim 74, apoppet sleeve or member 76, a poppet spring 78, a piston and valve body80, an externally-disposed first body o-ring seal 82, anexternally-disposed second body o-ring seal 84, an internally-disposedthird body o-ring seal 86, and an intensifier piston 88.

The first fasteners 44 threadably connect the stator assembly 40 andarmature spacer 64 to the poppet adapter 70. The second fastener 62threadably connects the armature 42 to the poppet valve 38 so that thearmature 42 and poppet valve 38 are displaced together as a unit. Thethird fasteners 66 threadably connect the poppet adapter 70 to the body80.

The armature spacer 64 has a thickness, measured along the longitudinalaxis 26, which is greater than the thickness of the armature 42 by aselected amount. As shown in FIG. 4, the second surface 54 of thearmature 42 is spaced from the poppet adapter 70 so that the armature 42and poppet adapter 70 stator 46 collectively define a lower armaturecavity 89 or gap therebetween. The size and position of each passage 58and collection groove 60 is carefully selected to ensure that it has alarge enough volume to adequately communicate, collect and drain dampingfluid with respect to cavities of the solenoid assembly 36, includingthe lower armature cavity 89, but also small enough to maximize theamount of flux paths in the stator 46 and armature 42 which arenecessary for adequate magnetic performance of the solenoid assembly 36.As shown in FIG. 6, the armature spacer 64 has a pair ofoppositely-facing planar first and second surfaces 90,92, an innerperipheral surface 94 and an outer peripheral surface 96. As shown inFIG. 4, the first surface 90 of the armature spacer 64 faces anddirectly contacts the stator assembly 40. The second surface 92 of thearmature spacer 64 faces and directly contacts the poppet adapter 70.The second surface 92 of the armature spacer 64 is provided with one ormore drain passages or slots 98 formed therein which extend from theinner peripheral surface 94 to the outer peripheral surface 96.Alternatively, the first surface 90 of the armature spacer 64 may beprovided with the drain passages or slots 98. During engine operation,the drain passages 98 of the armature spacer 64, in cooperation with thecommunicating, collecting and draining means 56, drain damping fluidwhich has been communicated to the upper and lower armature cavities57,89. The drain passages 98 of the armature spacer 64 are preferablysized to provide a selected restriction to flow of damping fluid duringengine operation in order to help facilitate damping of the motion ofthe armature 42 and poppet valve 38. The drain passages 98 of thearmature spacer 64 in cooperation with the communicating, collecting anddraining means 56 also drain damping fluid from the upper and lowerarmature cavities 57,89 after engine shutdown. If the actuating fluidand damping fluid are chosen to be engine lubricating oil, the drainpassages 98 of the armature spacer 64 are preferably adapted tocommunicate with the space enclosed by a cylinder head cover 99 as shownin FIG. 2. The fluid in this space communicates with an actuating fluidsump and is permitted to drain back to that sump.

As shown in FIGS. 4 and 7, the poppet adapter 70 has alongitudinally-extending centrally-disposed main bore 100 formedtherethrough. An internally-disposed annular peripheral groove 102 isformed on one end portion of the main bore 100. The poppet adapter 70also has a counterbore 104 formed on another end portion of the mainbore 100. An annular drain passage 106 is defined between the poppetsleeve 76 and the counterbore 104 of the poppet adapter 70. The poppetadapter 70 also has a drain passage 108 defined therein which intersectsthe annular drain passage 106 and laterally extends to an outerperipheral surface 110 of the poppet adapter 70. If the actuating anddamping fluid is chosen to be engine lubricating oil, the drain passage108 of the poppet adapter 70 is preferably adapted to communicate withthe space enclosed by the cylinder head cover 99 as shown in FIG. 2.

As shown in FIG. 4, the lower armature cavity 89 includes aclosely-controlled axial clearance or gap C₂ (for example, about 0.120millimeters or 0.00472 inches) is defined between the second surface 54of the armature 42 and the poppet adapter 70 when the armature 42 is inits electrically deenergized position. The clearance C₂ helps define thelower armature cavity 89 and also helps determine the amount of dampingimparted to the movable armature 42 by the damping fluid displaced fromthe clearance C₂. The magnitude of the clearance C₂ is selected inaccordance with the mass of the poppet valve 38 and the type (e.g.,viscosity characteristics) of damping fluid used.

The annular unit injector clamp 72 is provided for removably clampingeach unit injector 18 to the respective engine cylinder head 14.Preferably as shown in FIG. 7, the clamp 72 has an inner peripheralsurface 112, a pair of diametrically-opposed planar first and secondsurfaces 114,116 defined on the inner peripheral surface 112 in parallelrelationship, and a pair of diametrically-opposed semi-cylindrical slots118,120 formed in the inner peripheral surface 112. Each slot 118,120 islocated on an axis which is parallel to and located between the firstand second surfaces 114,116. As shown in FIG. 2, each slot 118,120 isadapted to engage a fastener 122,124 which threadably connects the clamp72 and unit injector 18 to the cylinder head 14 of the engine 12.

As shown in FIG. 3, the poppet shim 74 is positioned between the poppetadapter 70 and the poppet sleeve 76. The poppet shim 74 has a selectedthickness which determines the amount of upward lift or displacement ofthe poppet valve 38.

As shown in FIG. 4, the poppet sleeve 76 is slidably positioned in themain bore 100 of the poppet adapter 70 by a relatively loose fit. Theadapter o-ring seal 68 is positioned in the annular clearance betweenthe poppet sleeve 76 and the poppet adapter 70 and is seated in theannular peripheral groove 102 formed in the main bore 100 of the poppetadapter 70. The adapter o-ring seal 68 is provided in order to preventthe annular clearance from communicating actuating or damping fluiddirectly between the lower armature cavity 89 and the annular drainpassage 106. As shown in FIGS. 4 and 7, the poppet sleeve 76 is providedwith a centrally-disposed main bore 126 and one or more (preferably two)laterally-extending passages 128 which communicate actuating fluid ordamping fluid between the annular drain passage 106 and the main bore126. The size of the passages 128 are selected so that the passages 128function as fluid flow restrictions or fixed flow orifices in order todampen the motion of the poppet valve 38. The poppet sleeve 76 has oneend portion which defines an annular (preferably frusto-conical) seat129 around an entrance to the main bore 126 and an annular shoulder 130.

As shown in FIG. 3, one end of the poppet spring 78 contacts the annularshoulder 130 of the poppet sleeve 76 and the other end of the poppetspring 78 contacts the poppet valve 38. The poppet spring 78 ispreferably a helical compression spring and is provided as a means ordevice for biasing the poppet valve 38 and armature 42 axially away fromthe stator 46. The poppet spring 78 also biases the poppet sleeve 76 andpoppet shim 74 against the fixed poppet adapter 70 such that the poppetvalve 38 is normally unseated from the annular seat 129 defined on thepoppet sleeve 76.

As shown in FIG. 8, the poppet valve 38 has a first end portion 132, anintermediate portion 134 and a second end portion 136. As shown in FIG.4, the first end portion 132 contacts the second surface 54 of thearmature 42. The first end portion 132 preferably has a reduceddiameter, relative to the intermediate portion 134, and cooperates withthe poppet sleeve 76 to define an upper poppet valve cavity 138. Theupper poppet valve cavity 138 is in direct fluid communication with thelower armature cavity 89.

The intermediate portion 134 of the poppet valve 38 has an annularperipheral surface 140 and one or more (preferably two) passages 142.The annular peripheral surface 140 of the poppet valve 38 is positionedwithin the main bore 126 of the poppet sleeve 76 according to a selectedannular clearance C_(3a). This annular clearance preferably provides aslip fit between the poppet valve 38 and the poppet sleeve 76 and, forexample, may be a diametrical clearance of about 0.080 millimeters or0.00315 inches. The outer peripheral surface of the poppet sleeve 76 ispositioned in the main bore 100 of the poppet adapter 70 according to aselected diametrical clearance which is greater than the clearanceC_(3a). An upper annular peripheral groove 144 and an annular first orupper seat 146 are defined on the annular peripheral surface 140 of thepoppet valve 38. The width of the upper annular peripheral groove 144,measured along the longitudinal axis 26, is sized so that the upperannular peripheral groove 144 of the poppet valve 38 remains incontinuous fluid communication with the passages 128 of the poppetsleeve 76 over the entire selected displacement of the poppet valve 38.The shape of the upper seat 146 of the poppet valve 38 is preferablysemi-spherical but, alternatively, may be frusto-conical. The poppetvalve upper seat 146 is adapted to selectively engage or disengage theannular seat 129 formed on the poppet sleeve 76.

The second end portion 136 of the poppet valve 38 is preferably hollowto define a lower poppet valve cavity 148 shown in FIG. 4. The passages142 of the poppet valve 38 each have a selected fluid flow restrictiontherein and communicate damping fluid between the upper poppet valvecavity 138 and the lower poppet valve cavity 148. Part of the second endportion 136 of the poppet valve 38 is closely guided within the body 80to be discussed below. The second end portion 136 of the poppet valve 38includes an annular second or lower seat 149, an annular peripheralshoulder 150, and a lower annular peripheral groove 152. The shape ofthe poppet valve lower seat 149 is preferably frusto-conical. The firstand second seats 146,149 each have an effective area exposable tohydraulic pressure.

In one embodiment, the effective area of the first seat 146 is smallerthan the effective area of the second seat 149. In that embodiment, thenet hydraulic force acting on the poppet valve 38 assists the electricalforce of the actuator 36 in moving the valve 38 to from its firstposition to its third position. In another embodiment, the effectivearea of the first seat 146 is larger than the effective area of thesecond seat 149. In that embodiment, the net hydraulic force acting onthe poppet valve 38 assists the spring 78 in moving the valve 38 to fromits third position to its first position.

Preferably, the poppet sleeve 76 is loosely fitted within the poppetadapter 70 according to selected close positional and diametricaltolerances and the poppet valve 38 is relatively more tightly fitted inthe body 80 according to selected close positional and diametricaltolerances. This configuration helps accommodate possible misalignmentbetween the poppet sleeve 76 and the poppet valve 38 as the poppet valve38 travels along the longitudinal axis 26 of the unit injector 18. Theannular shoulder 150 formed on the poppet valve 38 contacts the otherend of the poppet spring 78. The lower seat 149 functions as a means forselectively opening or blocking the communication of high pressureactuating fluid to the intensifier piston 88. The upper seat 146functions as a means for selectively opening or blocking thecommunication of high pressure actuating fluid to a low pressure drainand the communication of low pressure damping fluid to the upper andlower armature cavities 57,89 and the upper and lower poppet valvecavities 138, 148.

The poppet valve 38 is movable between first, second and thirdpositions. For example, the total axial displacement of the poppet valve38 in one direction is about 0.25 millimeters or 0.0098 inches. Thefirst position of the poppet valve 38 is defined as the position atwhich the poppet valve lower seat 149 is normally seated on the body 80due to the bias of the poppet spring 78. At the first position of thepoppet valve 38, the poppet valve upper seat 146 is normally unseatedfrom the annular seat 129 of the poppet sleeve 76 by a selectedclearance.

When the stator assembly 40 is electrically energized, the armature 42is magnetically attracted towards the stator 46 so that the poppet valve38 moves axially upward (according to the orientation shown in FIG. 3)towards the third position. The third position of the poppet valve 38 isdefined as the position at which the upper seat 146 of the poppet valve38 is seated against the annular seat 129 of the poppet sleeve 76. Atthe third position of the poppet valve 38, the lower seat 129 of thepoppet valve 38 is unseated from the body 80.

Between the first and third positions, the poppet valve 38 assumes thesecond or intermediate position at which both the lower seat 149 and theupper seat 146 of the poppet valve 38 are unseated from the body 80 andthe poppet sleeve 76, respectively. At the second position of the poppetvalve 38, actuating fluid is exhausted through the upper annularperipheral groove 144, the passages 128, the annular drain passage 106,and the drain passage 108. Moreover, at the second position of thepoppet valve 38, damping fluid is communicated to the lower and upperarmature cavities 89,50 via the clearance C_(3a) if the viscosity of thedamping fluid is sufficiently low enough.

It is preferable that the clearance C_(3a) be located downstream (i.e.,with respect to the actuating fluid inlet passages 158) of the passages128 of the poppet sleeve 76. Thus, when the poppet valve 38 moves fromits third position (i.e, seated on its upper seat 146) and towards itsfirst position, a portion of the actuating fluid in the annular chamber163 is directed as damping fluid through the clearance C_(3a) while thepoppet valve assumes its second position and before the poppet valve 38assumes its first position (i.e., seated on its lower seat 149).

The solenoid assembly 36 is one of many possible embodiments of anelectronically-controlled actuator for selectively displacing the poppetvalve 38 from its first position, to its second position, to its thirdposition and vice versa. Alternatively, other types ofelectronically-controlled actuators, such as a piezoelectric actuator,may be substituted for the solenoid assembly 36.

A valve in the form of the poppet valve 38 provides at least twoadvantages over a spool valve in this application. First, when unseated,the poppet valve 38 opens up a relatively larger fluid flow area for asmall amount of axial displacement. Consequently, the poppet valve 38generally demands less electrical energy than a spool valve in order toadequately power the actuator 36. Second, the poppet valve 38 sealsbetter than a spool valve since the poppet valve 38 provides a positiveseal against each of its seats rather than some amount of diametricalclearance as a spool valve does with respect to a valve body. The poppetvalve 38 is also preferably of the single-stage (i.e., one-piece) type.A single-stage valve is advantageous over a two-stage or pilot-operatedvalve in this application because of lower cost, more flexibility inpackaging the unit injector for specific applications, and simplicity ofoperation.

As shown in FIGS. 3-5 and 8, the body 80 includes a pair ofoppositely-facing first and second blind bores 154,156, one or moreactuating fluid inlet passages 158, an actuating fluid intermediatepassage 160 communicating between the first and second blind bores154,156, and an external peripheral surface 162. The width of the lowerannular peripheral groove 152 of the poppet valve 38, measured along thelongitudinal axis 26, is sized so that it remains in continuous fluidcommunication with the inlet passages 158 of the body 80 over the entireselected displacement of the poppet valve 38.

The first blind bore 154 of the body 80 faces the armature 42 and isadapted to receive both the second end portion 136 and intermediateportion 134 of the poppet valve 38. The first blind bore 154 of the body80 and the second end portion 136 of the poppet valve 38 cooperate todefine an annular chamber 163. The actuating fluid communicated to theannular chamber 163 is at relatively low pressure when the poppet valve38 is at its first or second positions. The actuating fluid communicatedto the annular chamber 163 is at relatively high pressure when thepoppet valve 38 is at its third position. The first blind bore 154 isstepped to define a reduced diameter portion 164 and an annular(preferably frusto-conical) seat 166. The reduced diameter portion 164of the first blind bore 154 guides the second end portion 136 of thepoppet valve 38 according to a closely-controlled selected diametricalclearance C_(3b) which is less than the diametrical clearance C_(3a).The annular seat 166 of the body 80 is adapted to selectively engage anddisengage the lower seat 149 of the poppet valve 38.

The second blind bore 156 of the body 80 is adapted to receive thebarrel assembly 32 to be discussed below. As shown in FIG. 5, the secondblind bore 156 has an internally-disposed annular peripheral groove 168in which the third body o-ring seal is positioned. The third body o-ringseal 86 is provided as a means or device for positively sealing orisolating the actuating fluid present in the piston pump chamber 190from the fuel present in the piston chamber 192. This arrangement helpsprevent the fuel from diluting the lubricating and viscositycharacteristics of the actuating fluid and damping fluid. Alternatively,the third body o-ring seal 86 may be eliminated if the annularperipheral groove 168 functions as a collection space for leakage ofactuating fluid which is returned to the actuating fluid sump by a drainpassage (not shown). The second blind bore 156 also has a seat 170formed therein.

As shown in FIGS. 4, 5 and 8, the external peripheral surface 162 of thebody 80 includes axially-spaced first, second and third annularperipheral grooves 172,174,176. The external peripheral surface 162 alsoincludes oppositely-facing parallel planar first and second surfaces178,180 and a pair of transversely-extending shoulders 182,184 formedthereon. The second annular peripheral groove 174 is positioned axiallybetween the first and third annular peripheral grooves 172,176 anddefines an annular actuating fluid inlet passage with respect to thecylinder head 14. The first and second body o-ring seals 82,84 are eachpositioned in the respective first and third annular peripheral grooves172,176. The second body o-ring seal 84 is provided as a means or devicefor positively sealing or isolating the actuating fluid in the vicinityof the second annular peripheral groove 174 from the fuel in thevicinity of the barrel assembly.

The planar first and second surfaces 114,116 formed on the clamp 72 areadapted to engage the planar first and second surfaces 178,180 formed onthe body 80 in order to properly orient the unit injector 18 relative tothe engine cylinder head 14. The clamp 72 also contacts the shoulders182,184 of the body 80 in order to apply a clamping load thereto whenthe unit injector 18 is installed in the bore 16 of the cylinder head 14as shown in FIG. 2.

As shown in FIGS. 3 and 5, the intensifier piston 88 is slidablypositioned in the second blind bore 156 of the body 80. As shown in FIG.9, the intensifier piston 88 is a generally cup-shaped cylinder havingan outside diameter D₁ which corresponds to an effective cross-sectionalpumping area A₁. The intensifier piston 88 has a crown portion 186 and agenerally hollow cylindrical skirt portion 188. As shown in FIG. 5, thecrown portion 186 of the reciprocal intensifier piston 88 and the secondblind bore 156 of the body 80 collectively define an expandable andcontractible piston pump chamber 190. The skirt portion 188 of thereciprocal intensifier piston 88, the barrel assembly 32 and the secondblind bore 156 of the body 80 collectively define a contractible andexpandable piston chamber 192. The intensifier piston 88 also has firstand second stops 194,196 formed thereon. The first stop 194 ispreferably located on a free end of the crown portion 186 and is adaptedto engage and disengage the seat 170 of the body 80. The second stop 196is preferably located on a free end of the skirt portion 188 and isadapted to engage and disengage abutment with the barrel assembly 32.

As shown in FIGS. 3, 5, 9, and 10, the barrel assembly 32 includes abarrel 198, a ring retainer 200, a washer retainer 202, a plunger 204, aplunger spring 206, a one-way flow check valve 208 preferably in theform of a ball check, and an annular spring retainer 210.

As shown in FIG. 5, the barrel 198 includes a precision-formedcentrally-disposed longitudinally-extending main bore 212 and an outletpassage 214 communicating with the second blind bore 156 of the body 80.The outlet passage 214 includes an exit end portion having an annular(preferably frusto-conical) seat 216 formed thereon. The barrel 198 alsohas an outer peripheral surface in which an annular peripheral groove218 is formed.

One end portion of the barrel 198 facing the intensifier piston 88serves as a seat 219 for the second stop 196 of the intensifier piston88. As shown in FIG. 5, a selected axial clearance C₄ is providedbetween the barrel seat 219 and the second stop 196 of the intensifierpiston 88 in order to determine the maximum displacement or stroke ofthe intensifier piston 88.

The check valve 208 is positioned in the outlet passage 214 and isnormally biased against the seat 216 by a preload applied by the springretainer 210. The spring retainer 210 is preferably a split annularmember having a hole or indentation formed therein. The spring retainer210 is positioned in the annular peripheral groove 218 of the barrel 198so that it encircles not only the check valve 208 but also the barrel198 as well. The check valve 208 is seated in the relatively smallerhole in order to prevent the spring retainer 210 from rotating aroundthe barrel 198. This prevents the check valve 208 from eventually facingthe split portion of the spring retainer 210 where the check valve 208might work its way out.

Alternatively, the spring retainer 210 may be eliminated by forming anoutlet passage that exits the barrel 198 at a selected acute angle (for,example, about 55°). In this alternative embodiment, fluid pressure isrelied upon to seat the check valve 208 against the annular seat 216 ofthe barrel 198.

The plunger 204 is slidably positioned in the main bore 212 of thebarrel 198 by a close tolerance fit. The washer retainer 202 ispreferably connected to the plunger 204 by an interference fit.Moreover, the washer retainer 202 is fixed to the plunger 204 by thering retainer 200 which is positioned in an annular peripheral groove220 of the plunger 204. The plunger 204 has an outside diameter D₂ whichcorresponds to an effective cross-sectional pumping area A₂. Thediameter D₁ of the intensifier piston 88 is larger than the diameter D₂by a selected amount. For example, the ratio of the area A₁ to the areaA₂ is preferably about 7 to 1. This ratio can, of course, be varied totailor injection characteristics to the needs of a particular engine.The plunger spring 206 is positioned generally concentrically around theplunger 204 between the barrel 198 and the washer retainer 202. Theplunger spring 206 is preferably a helical compression spring whichbiases the plunger 204 and intensifier piston 88 upwardly against theseat 170 of the body 80. Preferably, the body 80 is connected to thebarrel 198 in correct angular alignment by a plurality of hardened steeldowels 222 which fit into respective longitudinally-extending dowelholes 224 defined in the body 80 and the barrel 198.

As shown in FIG. 3, the nozzle and tip assembly 34 includes a ballspring 226, a ball spacer 228, a one-way flow check valve 230 preferablyin the form of a ball check, a stop member 232, a plurality of hardenedsteel dowels 234, a stop pin 236, a needle check spring 238, a liftspacer 240, a sleeve 242, a fuel filter screen 244, an annular filterscreen retainer 246, a needle check 248, a plurality of dowels 250, aneedle check tip 252, a case 254, and first and second case o-ring seals256,258.

The stop member 232 is axially positioned between the barrel 198 and thesleeve 242. The stop member 232, barrel 198 and plunger 204 collectivelydefine a fuel pump chamber 260. The stop member 232 includes a fuelinlet passage 262 and one or more separate fuel discharge passages 264.Both the inlet passage 262 and the discharge passage(s) 264 communicatewith the fuel pump chamber 260. The inlet passage 262 has aninternally-disposed annular (preferably frusto-conical) seat 266generally facing the barrel 198. The check valve 230, ball spacer 228and ball spring 226 are positioned in the inlet passage 262 so that theball spacer 228 is positioned between the ball spring 226 and the checkvalve 230, the ball spring 226 is positioned between the barrel 198 andthe ball spacer 228, and the check valve 230 is positioned between theball spacer 228 and the annular seat 266 of the stop member 232. Theball spacer 228 locates one end of the ball spring 226 in force exertingrelation to the check valve 230 and also functions as a positive stopfor upward displacement of the check valve 230 towards the barrel 198.The ball spring 226 is preferably a helical compression spring whichnormally biases the check valve 230 against the annular seat 266.Alternatively, the ball spacer 228 and ball spring 226 may be eliminatedfrom the inlet passage 262 of the stop member 232.

As shown in FIGS. 3 and 5, the sleeve 242 is axially positioned betweenthe stop member 232 and the needle check tip 252. The sleeve 242 has agenerally centrally-disposed and longitudinally-extending bore 268, aradially-extending and stepped fuel inlet passage 270 which communicateswith the bore 268, and one or more fuel discharge passages 272 whichcommunicate with a respective fuel discharge passage 264 of the stopmember 232. The sleeve bore 268 has oppositely-facing first and secondcounterbores 274,276 and a reduced-diameter guide portion 278therebetween. The first counterbore 274 communicates with the inletpassage 262 of the stop member 232. The second counterbore 276 providessufficient fuel volume in order to prevent cavitation when the liftspacer 240 moves upwardly during an injection stroke. The stepped fuelinlet passage 270 defines an internally-disposed annular shoulder 279.The filter screen 244 is positioned within the fuel inlet passage 270against the annular shoulder 279 and is fixed thereto by the filterscreen retainer 246.

As shown in FIG. 3, the lift spacer 240 is axially positioned betweenthe stop pin 236 and the needle check 248. The needle check spring 238is positioned around the stop pin 236. The stop pin 236, needle checkspring 238 and lift spacer 240 are positioned in the sleeve bore 268 sothat the needle check spring 238 is preloaded and contacts both the stopmember 232 and the lift spacer 240. The needle check spring 238 is alsosupported by the guide portion 278 of the sleeve bore 268. As shown inFIG. 10, the lift spacer 240 has one or more flats or planar surfaces280 formed on its outer peripheral surface. The flats 280 providesufficient radial clearance between the lift spacer 240 and the sleevebore 268 in order to minimize the adverse pumping effect of the movablelift spacer 240.

As shown in FIG. 3, the needle check tip 252 is positioned between thesleeve 242 and the case 254. As shown in FIGS. 5 and 11, the needlecheck tip 252 includes a generally centrally-disposedlongitudinally-extending blind bore 281, having an internally-disposedannular (preferably frusto-conical) seat 282 defined thereon, one ormore discharge passages 283, a cardioid chamber 284, and an annulardischarge passage 285. The needle check 248 and needle check tip 252 arepreferably of the valve-closed-orifice type. One end portion of theneedle check tip 252 defines at least one but preferably a plurality offuel injection spray orifices 286. The needle check spring 238 normallybiases the lift spacer 240 and needle check 248 downwardly so that theneedle check 248 is seated against the annular seat 282 of the needlecheck tip 252. Preferably, the needle check tip 252 further includes anannular seat portion 288, a reduced diameter stem portion 290, and anintermediate diameter guide portion 292 therebetween. The dowels 250 andcorresponding dowel holes 296 formed in both the needle check tip 252and the sleeve 242 connect the needle check tip 252 to the sleeve 242 incorrect angular relationship.

The case 254 has multi-stepped longitudinally-extending first, secondand third bores 298,300,302, an internally-disposed annular seat 304, anexternally-disposed annular seat 306, a fuel inlet passage in the formof one or more radially-extending fuel inlet holes 308, and first andsecond outer peripheral annular grooves 310,312.

The third bore 298 is located at one end portion of the case 254 betweenthe externally-disposed annular seat 306 and the internally-disposedannular seat 304. The annular seat portion 288 of the needle check tip252 is seated against the internal annular seat 304 of the case 254 inorder to positively seal combustion gas from fuel. The external annularseat 306 of the case 254 is adapted to seal against a seat formed in theunit injector bore 16 of the cylinder head 14 or a sleeve positionedbetween the unit injector 18 and the unit injector bore 16 of thecylinder head 14. The intermediate diameter guide portion 292 of theneedle check tip 252 is positioned entirely within the third bore 302 ofthe case 254. The elongated reduced diameter stem portion 290 of theneedle check tip 252 projects outwardly through the case 254 via thethird bore 302. The stepped configuration of the needle check tip 252 isadvantageous because it provides sufficient material for strength in thevicinity of the mating seats 288,304 of the needle check tip 252 and thecase 254 which is subjected to high stresses caused by high pressurefuel in the cardioid chamber 284. The intermediate diameter guideportion 292 of the needle check tip 252 provides a gradual transitionwithin the envelope of the case 254 to the reduced diameter stem portion290. Thus, the cylinder head bore through which the reduced diameterstem portion 290 passes can be a relatively small and constant diameterwhich does not appreciably diminish the strength of the cylinder head14.

The fuel inlet holes 308 communicate with an annular fuel inlet passage314 defined by a clearance between an inside wall of the case 254 andouter peripheral surfaces of the barrel 198, stop member 232, and sleeve242. The fuel inlet holes 308 of the case 254 not only serve as a meansor device for admitting fuel into the unit injector but also serve asthe sole means or device for temporarily engaging the tangs of a wrenchused to tighten the internal screw threads of the case 254 onto theexternal screw threads of the body 80.

The first and second case o-ring seals 256,258 are positioned in therespective first and second outer peripheral annular grooves 310,312 ofthe case 254. The first case o-ring seal 256 is provided around anintermediate portion of the unit injector 18 in order to seal actuatingfluid from fuel. The second case o-ring seal 258 is provided around alower end portion of the unit injector 18 in order to seal combustiongas originating from the engine combustion chamber from fuel in thevicinity of the barrel assembly 32.

The cup-shaped case 254 encloses and retains the needle check tip 252,needle check 248, sleeve 242, stop member 232, barrel 198, plunger 204,plunger spring 206 and intensifier piston 88 against the body 80.Preferably the case 254 is removably connected to the body 80 by athreaded connection.

Referring primarily to FIG. 12, but also FIGS. 1 and 2, thehydraulically actuating fluid and damping fluid supplying means 20comprises a main actuating fluid circuit which preferably includes anactuating fluid sump 316, a pickup screen-type filter 318, a one-wayflow check valve 320, an actuating fluid transfer pump 322, an actuatingfluid cooler 324, one or more actuating fluid filters 326, a means ordevice 328 for bypassing actuating fluid with respect to the fluidfilters 326, a priming or engine starting reservoir 330, arelatively-high-pressure actuating fluid pump 332, first and second highpressure actuating fluid manifolds 334,336, means or device 338 forcontrolling the creation of Helmholtz resonance of pressure wavesbetween the manifolds 334,336 and between the pump 332 and eithermanifold 334,336, and a means or device 340 for controlling the pressurelevel in the manifolds 334,336.

Preferably, the fluid chosen for the actuating fluid is not fuel but isa liquid fluid having a relatively higher viscosity than fuel under thesame conditions. For example, the actuating fluid may be enginelubricating oil. In this example, the actuating fluid sump 316 is theengine lubrication oil sump.

The check valve 320 is provided as an anti-siphon valve in order to helpmaintain actuating fluid in the circuit. After engine shutdown, thecircuit remains primed with sufficient actuating fluid in order tofacilitate quick starting of the engine 12.

The transfer pump 322 is of a conventional design. For example, thetransfer pump 322 may be a gearotor pump which develops a relatively lowpressure (for example, about 413 kPa or 60 psi).

The filters 326 are preferably of the replaceable element type. Thefilter bypassing means 328 includes a bypass line 342 connected upstreamand downstream of the fluid filters 326. The filter bypassing means 328further includes a filter bypass valve 344, positioned in the bypassline 342, and a return line 346 connected between the bypass line 342and the sump 316. The filter bypassing means 328 further includes anactuating fluid pressure regulator 348 positioned in the return line346.

During engine operation, if the fluid filters 326 become plugged withdebris, the pressure downstream of the fluid filters 326 will begin todecrease. If that pressure falls below a selected level (for example,about 138 kPa or 20 psi), the filter bypass valve 344 is activated whichpermits the actuating fluid to bypass the fluid filters 326 and continueflowing towards the priming reservoir 330. The pressure regulator 348 isprovided as a means for preventing the actuating fluid which is upstreamof the pump 332 from exceeding a selected pressure (for example, about345 kPa or 50 psi). If that selected pressure is exceeded, the excessactuating fluid is returned to the sump 316.

Downstream of the fluid filters 326, the actuating fluid is split intofirst and second branch passages 350,352 if engine lubricating oil ischosen as the actuating fluid. Most of the lubricating oil flows (forexample, about 57 liters per minute or 15 gallons per minute) into thefirst branch passage 350 which supplies the engine lubricating system(not shown). The remainder of the lubricating oil (for example, about 15liters per minute or 4 gallons per minute), amounting to about 25-33% ofthe total flow, flows into the second branch passage 352 whichcommunicates with the priming reservoir 330 of the main actuating fluidcircuit.

The priming reservoir 330 is provided as a means for priming and therebyfacilitating rapid pressurization of the high pressure pump 332 duringengine startup. The priming reservoir 330 is positioned upstream of thepumping chamber(s) of the high pressure pump 332 and is arranged incloser fluid communicating proximity to the pump 332 than to theseparate sump 316. For example, the priming reservoir 330 may beintegrally formed with a front cover (not shown) of the engine 12.Alternatively, the priming reservoir 330 may be integrally formed withthe high pressure pump 332. At or near the highest elevation of thefluid level of the priming reservoir 330 there is a return line 354 witha selected flow restriction 356 therein. Preferably, the flowrestriction 356 is a fixed flow area orifice. The return line 354 andflow restriction 356 are provided in order to bleed air from the primingreservoir 330 and direct the air back to the sump 316 where it may bevented to atmosphere.

Upstream of the cooler 324 is a cooler/filter bypass line 358 whichcompletely bypasses the cooler 324 and fluid filters 326 andcommunicates directly with the priming reservoir 330. The cooler/filterbypass line 358 is provided as a means or device for automaticallymaking up or replenishing any actuating fluid that is deficient in thepriming reservoir 330 during cold engine operating conditions when theviscosity of the actuating fluid is relatively higher. The cooler/filterbypass line 358 has a one-way flow check valve 360 disposed therein.

During cold temperature operation of the hydraulically actuating fluidand damping fluid supplying means 20, the check valve 360 opens fluidflow through the cooler/filter bypass line 358 and towards the primingreservoir 330 if the fluid pressure in the priming reservoir 330 is lessthan the fluid pressure in the outlet of the transfer pump 322 by aselected amount. This difference in pressure causes the check valve 360to open to some corresponding extent and feed a portion or all of theactuating fluid directly to the priming reservoir 330 without beingfiltered. Flow through the cooler/filter bypass line 358 is activatedwhenever the second passage 352 leading to the priming reservoir 330 isnot able to completely fill the priming reservoir 330. When the pressurein the priming reservoir 330 reaches a selected level relative to theoutlet of the transfer pump 322, the check valve 360 is closed and flowof completely filtered actuating fluid is resumed to the primingreservoir 330.

At or near the bottom (lowest elevation) of the priming reservoir 330,there is a pump supply passage 362 which is connected to an inlet of thehigh pressure pump 332. Preferably, the highest level or elevation ofthe actuating fluid in the priming reservoir 330 is higher than thehighest level of actuating fluid in the pumping chamber(s) of the highpressure pump 332 in order to ensure that the high pressure pump 332remains completely primed with actuating fluid.

Preferably, in order to minimize cost, the high pressure pump 332 is afixed displacement axial piston pump which is mechanically driven by theengine 12. The high pressure pump 332 operates in conjunction with aprimary variable pressure regulator to be discussed below.Alternatively, the high pressure pump 332 may be a variable displacementaxial piston pump without the primary variable pressure regulator. In aHEUI fuel injection system 10 for a vee-type engine 12, the highpressure pump 332 is preferably located at the front of the engine 12 ator near the apex of the vee formed by the pair of cylinder heads 14. Theoutlet of the high pressure pump 332 communicates with first and secondmanifold supply passages 364,366. Each of the first and second manifoldsupply passages 364,366 communicates with a respective manifold 334,336.

Preferably, the manifold pressure controlling means 340 includes anelectronically-controlled primary pressure regulator 368. The primarypressure regulator 368 is connected between the outlet of the highpressure pump 332 and a return line 370 which communicates with the sump316. The primary pressure regulator 368 is provided as a means or devicefor varying the pressure in the manifolds 334,336 between selectedlimits (for example, about 2067 to 20670 kPa or 300 to 3000 psi). Byvarying the actuating fluid pressure in the manifolds 334,336, theinjection pressure of the fuel delivered by the unit injectors 18 isconsequently varied. The manifold pressure controlling means 340 furtherincludes a pressure relief valve 372 which backs up the primary pressureregulator 368 and protects the manifolds 334,336 from exceeding aselected pressure (for example, about 27560 kPa or 4000 psi.

When activated, the primary pressure regulator 368 and/or pressurerelief valve 372 direct excess actuating fluid through the return line370 that communicates with the sump 316. Fluid leakage in the highpressure pump 332 is communicated through a case drain passage 374 whichis connected to the return line 370 communicating with the sump 316. Anactuating fluid pressure sensor 376 is provided in at least one of themanifolds 334,336 and sends a signal S₆ back to the electroniccontrolling means 24.

The Helmholtz resonance controlling means 338 includes a one-way flowcheck valve 378,380 positioned in each of the first and second manifoldsupply passages 364,366 connecting the high pressure actuating fluidpump 332 with each of the manifolds 334,336. The Helmholtz resonancecontrolling means 338 further includes a bypass line 382,384 having aselected flow restriction 386,388 therein which is connected in parallelwith each check valve 378,380. Alternatively, the selected flowrestriction 386,388 may be integrally formed with the check valve378,380 to constitute an orificed check valve. Preferably, each flowrestriction 386,388 is a fixed flow area orifice but, alternatively, maya variable flow area orifice.

The Helmholtz resonance controlling means 338 is provided in order tocontrollably minimize or prevent the creation of Helmholtz resonance ofpressure waves which would naturally occur between the twointerconnected high pressure manifolds 334,336 and also the pump 332 andeither manifold 334,336. Controlling Helmholtz resonance helps tomaintain a more uniform pressure over time in each manifold 334,336 at aconstant pressure setting of the primary pressure regulator 368. Thecheck valves 378,380 isolate fluid communication from one manifold tothe other. The bypass line 382,384 and flow restrictions 386,388minimize fluid communication from one manifold 334,336 to the otherwhich dissipates fluid energy released when its respective check valve378,380 is closed. The bypass lines 382,384 and flow restrictions386,388 also perform three other functions. First, they function as ameans or device for bleeding down the pressure in each manifold 334,336during engine operation after the electronic control module 454 signalsthe primary pressure regulator 368 to lower the pressure in themanifolds 334,336. They also function as a means or device for bleedingdown the high pressure in the manifolds after engine shutdown so thatthe unit injectors 18 may be removed for servicing without spillingactuating fluid from the engine 12. Moreover, if the actuating fluid wasnot bled down from the manifolds 334,336 after engine shutdown and uponrestarting the engine 12, the unit injectors 18 would tend to produceblack smoke or other undesirable emissions and also cause a very audibleknocking noise. Second, they function as a means or device forequalizing the pressure of the actuating fluid communicated to both thefirst and second manifolds (334,336) during operation of the fuelinjection system (10). Third, they form part of the hydraulic makeupcircuit described immediately below. The flow area of each flowrestriction 386,388 and mass and displacement of the check valves378,380 are chosen in accordance with the system pressure, flowrequirements, operating frequency, and hydraulic configuration of theHEUI fuel injection system 10.

The actuating fluid circuit also includes a means or device 390 forautomatically making up or replenishing the void in each manifold334,336 which appears after engine shutdown due to cooling andcontraction of actuating fluid and/or precipitation of entrained airfrom the actuating fluid. Without the compensating effect of the makingup means 390, the lost volume of actuating fluid in each manifold334,336 would delay engine startup until the high pressure pump 332 isable to refill the lost volume in the manifolds 334,336. The making upmeans 390 preferably includes an actuating fluid siphon passage 392. Thesiphon passage 392 bypasses the inlet of the high pressure pump 332 andis connected directly between the priming reservoir 330 and themanifolds 334,336. The siphon passage has a one-way flow check valve 394therein which permits flow from the priming reservoir 330 to themanifolds 334,336. The making up means 390 also includes the bypasslines 382,384 and flow restrictions 386,388 which supply actuating fluidto a respective manifold 334,336.

Preferably, one actuating fluid manifold 334,336 is provided for andassociated with each cylinder head 14 having a bank of unit injectors18. For example, in a vee-type engine 12, two actuating fluid manifolds334,336 are provided. In the embodiment shown in FIG. 2, each actuatingfluid manifold 334,336 is integrally formed with an air intake manifold396 and this combined unit is bolted or otherwise connected to therespective cylinder head 14. Alternatively, each actuating fluidmanifold 334,336 may be a separate component which is connected to therespective cylinder head 14. Alternatively, each actuating fluidmanifold 334,336 may be integrally formed with the respective cylinderhead 14. One advantage of integrating the actuating fluid manifolds334,336 as internal passages of the engine 12 is the elimination ofexternal high pressure actuating fluid lines which would add cost andcomplicate assembly and reliability of the HEUI fuel injection system 10relative to the engine 12. Another advantage is the neater or relativelyuncluttered and more esthetically appealing appearance of the engine 12which makes it easier to access for service or repair. The unclutteredappearance of the engine also makes it easier to adapt or install forvarious applications.

Each actuating fluid manifold 334,336 has one common rail passage398,400 and a plurality of rail branch passages 402 communicating withthe common rail passage 398,400. The number of rail branch passagescorresponds to the number of unit injectors 18 positioned in eachcylinder head 14. Each common rail passage 398,400 extends across therespective cylinder head (14) in spaced and parallel relation to theentire bank of unit injectors 18 positioned in each cylinder head 14. Asshown in FIG. 2, each of the rail branch passages 402 also communicateswith a respective unit injector bore 16 formed in the cylinder head 14and the second annular peripheral groove 174 defined in the respectiveunit injector 18. The annular peripheral groove 174 of the unit injector18 and bore 16 define an annulus which ensures that the high pressureactuating fluid communicated by the rail branch passage 402 to the unitinjector 18 exerts a substantially uniform or balanced pressure all theway around the outer periphery of the unit injector 18. This preventsthe unit injector 18 from experiencing an unbalanced high pressure sideload if there were no annulus between the rail branch passage 402 andthe actuating fluid inlet passages 158 of the unit injector 18.

Referring primarily to FIG. 13, but also FIGS. 1 and 2, the fuelsupplying means 22 comprises a fuel injection circuit 404 which includesa fuel tank 406, a fuel supply line 408, a fuel transfer and primingpump 410, a means or device 412 for conditioning the fuel, a fuelmanifold 414,416 provided for and associated with each cylinder head 14,and one or more fuel return lines 418,420.

Preferably, the fuel conditioning means 412 includes a fuel heater 422,a fuel filter 424, and a fuel/water separator 426. Fuel is drawn by thefuel transfer pump 410 from the tank 406 and flows through the fuelconditioning means 412 where it is heated to a selected temperature,filtered, and separated from water. The fuel conditioning means 412 hasa fuel outlet passage 428 which is connected to a tee 430. The tee 430divides the fuel flow into two portions and communicates with a pair offuel manifold supply passages 432,434. Each fuel manifold supply passage432,434 communicates with a respective fuel manifold 414,416 defined ineach of the cylinder heads 14. As shown in FIG. 2, each fuel manifold414,416 is in the form of a common fuel rail passage which is preferablyformed as an internal passage of the respective cylinder head 14. Eachcommon fuel rail passage partially but directly intersects each unitinjector bore 16 associated with that cylinder head 14 and communicateswith the second annular peripheral groove 174 of the unit injector 18associated with that unit injector bore 16.

The fuel conditioning means 412 further includes another tee 436positioned upstream of the tee 430 at a location which is preferably ator near the highest point or elevation in the fuel flow circuit. Onebranch of the another tee 436 is connected to an air-bleed returnpassage 438 which returns trapped air back to the fuel tank 406. Theair-bleed return passage 438 may include a selected flow restriction 442in order to minimize the amount of fuel flow through the air-bleedreturn passage 438. As shown in FIG. 13 but not FIG. 1, the fuel returnlines may merge into a common return line 444 which communicates withthe fuel tank 406. A selected flow restriction 448, preferably in theform of a fixed flow area orifice, is positioned near the outlet of eachfuel manifold 414,416 in order to help maintain the pressure in thatfuel manifold at a selected pressure (for example, about 276 to 413 kPaor 40 to 60 psi) during engine operation. Moreover, a pressure regulator450 which may also function as an anti-siphon valve may be positioned inthe return line 444 as a substitute for or as an addition to theindividual flow restriction 448. The fuel conditioning means 412 mayalso include a warning device 452 in the form of a light and/or alarmvisible to an engine operator which indicates when the fuel filter 424requires servicing.

Referring to FIG. 1, the electronic controlling means 24 includes aprogrammable electronic control module 454 and a means or device fordetecting at least parameter and generating a parameter indicativesignal (S₁₋₅,7-8), hereinafter referred to as an input data signal,which is indicative of the parameter detected. The detecting andgenerating means preferably includes one or more conventional sensors ortransducers which periodically detect one or more parameters such asengine and/or transmission operating conditions and generatecorresponding input data signals which are sent to the electroniccontrol module 454. Preferably, such input data signals include enginespeed S₁, engine crankshaft position S₂, engine coolant temperature S₃,engine exhaust back pressure S₄, air intake manifold pressure S₅, andthrottle position or desired fuel setting S₇. Moreover, if the engine 12is coupled to an automatic transmission, the input data signals may alsoinclude a transmission operating condition indicative signal S₈ which,for example, indicates the gear setting of the transmission.

The electronic control module 454 is programmed with variousmulti-dimensional control strategies or logic maps which take intoaccount the input data and then compute a pair of desired or optimaloutput control signals S₉,S₁₀. One output control signal S₉ is theactuating fluid manifold pressure command signal. This signal isdirected to the primary pressure regulator 368 in order to adjust theoutput pressure of the pump 332 which in turn adjusts the pressure ofthe actuating fluid in the manifolds 334,336 to a desired amount.Adjustment of the actuating fluid pressure has the effect of directlyadjusting the fuel injection pressure independent of engine speed. Thus,the output control signal S₉ can also be considered the fuel injectionpressure command signal.

Accurate control of the actuating fluid pressure helps ensure accuratecontrol of fuel injection timing and quantity. In order to accuratelycontrol the actuating fluid pressure, a closed-loop feedback circuit isprovided. A sensor is provided for detecting the pressure of thehydraulically actuating fluid supplied to the unit injectors 18 and forgenerating a pressure indicative signal S₆ indicative of the pressuredetected. The sensor is preferably positioned in at least one of themanifolds 334,336 and periodically samples the actual pressure.Preferably, the frequency of sampling is selected in order to detect amean or average pressure which is not too sensitive to insignificanttransient effects. The sensor generates a corresponding input datasignal S₆ which is sent to the electronic control module 454. Theelectronic control module 454 compares the actual actuating fluidpressure with the desired or optimal setting and makes any necessarycorrection to the output control signal S₉.

The other output control signal S₁₀ is the fuel delivery command signalwhich is supplied to the electronic actuator assembly 36 of eachselected unit injector 18. The fuel delivery command signal S₁₀determines the time for starting fuel injection and the quantity of fuelinjected during each injection phase. Preferably, the fuel deliverycommand signal produced by the electronic control module 454 is fed toan electronic drive unit (not shown). The electronic drive unit producesa selected waveform that is directed to the actuator assembly 36 of theunit injector 18.

For example, the waveform produced by the electronic drive unit may be atwo-step function. The first step of the function may be a signal ofabout seven amperes which is sufficient to rapidly move the armature 42and poppet valve 38 to their third position which permits communicationof high pressure actuating fluid to the intensifier piston 88. Thesecond step of the function may be a relatively smaller magnitude signalof about half of the magnitude of the first step (e.g., about 3.5amperes), which is sufficient to maintain the armature 42 and poppetvalve 38 in their third position until the fuel delivery command signalis ended by the electronic control module 454. Preferably the electroniccontrol module 454 directly drives the primary pressure regulator 368without the need for an intermediate electronic drive unit.

Industrial Applicability

The HEUI fuel injection system 10 uses an actuating and damping fluidwhich is separate from the fuel used for injection into the engine 12.The advantages of using engine lubricating oil rather than fuel as thesource for the actuating fluid and damping fluid are as follows. Enginelubricating oil has a higher viscosity than fuel and therefore the highpressure actuating fluid pump 332 and body assembly 30 of the unitinjector 18 do not require the degree of precision clearances oradditional pumping capacity that would be required in order to pump fuelwithout excessive leakage particularly when starting an engine when thefuel is still relatively hot. The engine lubricating oil provides betterlubrication than does, for example, diesel fuel. Such lubrication isespecially needed in the guide and seats of the poppet valve 38. Theengine lubricating oil is also able to utilize the oil drain paths tothe sump 316 that normally exist in a conventional engine whereas fuelused as actuating and damping fluid would require additional passages orexternal lines for draining that fuel back to the fuel tank. Such oildrain paths as the relatively large air space within the cylinder headcover 99 do not present a restriction to flow. Thus, at the end ofinjection, the pressure spike which naturally occurs is quicklydissipated rather than possibly being reflected back to the solenoidassembly 36 where it could damage relatively delicate components. Theventing of high pressure actuating fluid in drain paths which areseparate from the fuel supply paths helps prevent variation in fueldelivery and timing of injection between various unit injectors 18.

An efficient method or strategy for starting the engine 12 will now bedescribed. While the engine 12 is initially cranked by an auxiliarypower source, such as a battery and starter motor (not shown), theelectronic control module 454 monitors the actuating fluid manifoldpressure S₆. The electronic control module 454 is programmed so that itdoes not electrically energize the solenoid assembly 36 of any unitinjector 18 with a fuel delivery command signal S₁₀ until the actuatingfluid manifold pressure S₆ increases to at least a selected minimumpressure level. During this time, the cranking engine 12 mechanicallydrives the high pressure actuating fluid pump 332 to rapidly build uppressure in the actuating fluid manifolds 334,336 which serve aspressure accumulators.

Preferably, the selected minimum pressure level of the actuating fluidnecessary to trigger energization of the unit injectors 18 is thatminimum pressure required to actuate at least one fuel injection by aunit injector 18. The selected minimum pressure level varies with thetemperature or viscosity of the actuating fluid and generally would behigher under cold engine starting conditions compared to hot enginestarting conditions. The selected minimum pressure level also depends onthe actual hydraulic configuration of the unit injector 18 which coversparameters such as the nozzle opening pressure of the nozzle and tipassembly 34 and the pressure intensification ratio between theintensifier piston 88 and the plunger 204.

A sensor (not shown) for detecting the temperature or viscosity of theactuating fluid may be provided. Alternatively, the sensor may detectanother engine parameter, such as engine coolant temperature, whichindirectly indicates the temperature or viscosity of the actuatingfluid. In either embodiment, the temperature or viscosity indicativesignal generated by the sensor is sent to the electronic control module454 which then determines or selects an appropriate minimum pressurelevel according to the temperature or viscosity indicative signal. Afterat least one unit injector 18 has injected fuel, the engine 12 fires sothat the engine speed rapidly increases resulting in increased pumpingefficiency of the high pressure pump 332. An advantage of the aboveengine starting strategy is the ability to minimize the size (i.e.,pumping capacity) of the high pressure actuating fluid pump 332 based onwhat is required to achieve quick engine starts. Minimizing the size ofthe pump 332 reduces cost and also parasitic horsepower losses of theengine 12. The above engine starting strategy is applicable to anyhydraulically actuated fuel system, including the HEUI fuel injectionsystem 10, utilizing oil, fuel or some other fluid as the actuatingfluid.

Various alternative methods of starting the fuel system 10 or engine 12will now be discussed. A first alternative method comprises the step ofcranking the engine 12 so that the pump 332 is pressurizing actuatingfluid used to hydraulically actuate a plurality ofhydraulically-actuated electronically-controlled unit injectors 18. Themethod further comprises the step of the electronic control module 454electrically actuating each unit injector 18 sequentially one at a timeto cause fuel injection only after a selected period of time has elapsedduring pressurization of the actuating fluid. A second alternativemethod comprises the steps of pressurizing actuating fluid used tohydraulically actuate a plurality of hydraulically-actuatedelectronically-controlled unit injectors, electrically actuating aselected number of unit injectors sequentially one at a time to causefuel injection only after a selected period of time has elapsed duringpressurization of the actuating fluid, and electrically actuating allthe unit injectors sequentially one at a time to cause fuel injectionafter the fuel system 10 or engine 12 is started. A third alternativemethod comprises the steps of pressurizing actuating fluid used tohydraulically actuate a plurality of hydraulically-actuatedelectronically-controlled unit injectors, electrically actuating aselected number of unit injectors sequentially one at a time to causefuel injection during startup of the fuel system 10 or engine 12, andelectrically actuating all the unit injectors sequentially one at a timeto cause fuel injection after the fuel system 10 or engine 12 isstarted. A fourth alternative method comprises the steps of pressurizingactuating fluid used to hydraulically actuate a plurality ofhydraulically-actuated electronically-controlled unit injectors,electrically actuating a selected number of unit injectors sequentiallyone at a time to cause fuel injection only after a selected period oftime has elapsed during pressurization of the actuating fluid, andgradually increasing the number of unit injectors that are electricallyactuated sequentially one at a time to cause fuel injection. If the fuelsystem 10 or engine 12 stalls, the number of unit injectors 18 that areelectrically actuated sequentially one at a time may be decreased andthe method of starting is repeated.

The operation of one unit injector 18 after engine startup will now bedescribed. Referring to FIGS. 1, 2 and 13, fuel is supplied at arelatively low pressure (for example, about 276 to 413 kPa or 40 to 60psi) to the unit injector 18 by the respective fuel manifold 416.Referring to FIGS. 3 and 5, the fuel flows through the case fuel inletholes 308, the annular passage 314, the sleeve fuel inlet passage 270,the fuel filter screen 244, and then the sleeve bore 268. Therelatively-low-pressure fuel unseats the check valve 230 in oppositionto the force of the compressed ball spring 226 when the solenoidassembly 36 is in its de-energized state and the pressure in the fuelpump chamber 260 is lower than the pressure upstream of the check valve230 by a selected amount. While the check valve 230 is unseated, thefuel pump chamber 260 is refilled with fuel.

While the solenoid assembly 36 is in its de-energized state, the poppetvalve 38 is at its first position blocking fluid communication betweenthe actuating fluid inlet passage 158 and the piston pump chamber 190while opening communication between the piston pump chamber 190 and theupper annular peripheral groove 144, passage 128 and drain passage 108that communicate with the sump 316. With negligible fluid pressure inthe piston pump chamber 190, the plunger spring 206 pushes upwardlyagainst the plunger 204 and intensifier piston 88 so that the first stop194 contacts the seat 170.

In order to start injection, a fuel delivery command signal S₁₀ isgenerated by the electronic control module 454 and delivered to theelectronic drive unit. The electronic drive unit generates a preselectedwaveform to the solenoid assembly 36 of a selected unit injector 18. Thesolenoid assembly 36 is electrically energized so that the armature 42is magnetically drawn towards the stator 46.

The poppet valve 38 is also pulled by the moving armature 42. The poppetvalve 38 initially moves to its second position where its lower seat 149opens fluid communication between the actuating fluid inlet passage 158and the piston pump chamber 190 while maintaining fluid communicationbetween the piston pump chamber 190 and the upper annular peripheralgroove 144, passage 128 and drain passage 108. During this portion ofthe displacement of the poppet valve 38, the relatively-high-pressureactuating fluid communicated from the inlet passage 158 is reduced torelatively low pressure in the annular chamber 163 and a portion of itis exhausted back to the sump 316 through the restricted passages 128 ofthe poppet sleeve 76. During hot engine operating conditions, a portionof the depressurized actuating fluid is used as damping fluid which canleak past the clearance C_(3a) in order to decelerate the velocity ofthe poppet valve 38 as it approaches its third position. Moreover,damping fluid which is displaced from the upper poppet valve cavity 138to the lower poppet valve cavity 148 via the restrictive passages 142also tends to decelerate the velocity of the poppet valve 38 as itapproaches its second and third positions.

While the poppet valve 38 moves from its first position to its secondposition, the restricted passages 128 function as a means or device forpermitting some buildup of pressure in the piston pump chamber 190 butalso for draining enough fluid flow to the sump 316 so that the start offuel injection is delayed. This sequence of operation ensures that thetransitory and somewhat unpredictable initial motion of the poppet valve38 from its stationary first position to its second position is isolatedwith respect to or does not coincide with the time period at which fuelinjection starts. The chosen size of the restrictive passages 128 is acompromise between being large enough to quickly terminate fuelinjection when the poppet valve 38 moves from its third position to itssecond position and being small enough to minimize the waste ofactuating fluid being drained back to the sump 316 while the poppetvalve 38 moves from its first position to its second position.

The poppet valve 38 continues to move to its third position where thelower seat 149 continues opened fluid communication between the inletpassage 158 and the piston pump chamber 190 while the upper seat 129blocks fluid communication between the piston pump chamber 190 and theupper annular peripheral groove 144, passage 128 and drain passage 108.Actuating fluid at a relatively high pressure (for example, about 20670kPa or 3000 psi) which flows through the inlet passage 158 is trapped inthe annular chamber 163, intermediate passage 160 and piston pumpchamber 190 and thereby hydraulically exerts a driving force on theintensifier piston 88.

High pressure actuating fluid which may leak from the inlet passages 158and through the closely controlled clearance between the second endportion 136 of the poppet valve 38 and the reduced diameter guideportion 164 of the body 80 communicates with the lower poppet valvecavity 148, the passages 142, the upper poppet valve cavity 138, thelower armature cavity 89, and the drain passages 98 of the armaturespacer 64.

The one-way check valve 208, in cooperation with the reciprocalintensifier piston 88, is provided as an inexpensive and easy toassemble means or device for positively evacuating fuel from the pistonchamber 192 during a downward pumping stroke of the intensifier piston88. Such fuel tends to leak into the piston chamber 192 in betweensuccessive pumping strokes of the intensifier piston 88 and plunger 204by way of the closely controlled annular clearance between the plunger204 and the main bore 212 of the barrel 198. Any fuel leakage whichcollects in the piston chamber 192 is effectively pumped out through theone-way check valve 208 by the downward motion of the intensifier piston88. The fuel which is evacuated from the piston chamber 192 in thismanner is prevented by the one-way check valve 208 from directlyreentering the piston chamber 192. The evacuation of fuel in the pistonchamber 192 during engine operation eliminates or minimizes fluidresistance or fluid pressure therein which would have adversely affectedthe intended motion of the intensifier piston 88 and plunger 204.Moreover, large pressure pulses generated in the piston chamber 192 bythe downward motion of the intensifier piston 88 are minimized oreliminated. The elimination of such large pressure pulses helps preventdamage to fuel filters located upstream of the unit injector 18 and alsopossible uncontrolled variations in fuel injection rate among other unitinjectors 18 of the engine.

The high pressure actuating fluid displaces the intensifier piston 88and plunger 204 in opposition to the force generated by the compressedplunger spring 206. The fuel trapped in the fuel pump chamber 260 ispressurized to a level which is a function of the pressure of theactuating fluid in the intensifier piston pump chamber 190 and the ratioof effective areas A₁ /A₂ between the intensifier piston 88 and theplunger 204. This pressurized fuel flows from the fuel pump chamber 260and through the discharge passages 264,272,283,285 where it acts on theneedle check 248 in opposition to a preload exerted by the needle checkspring 238. The pressurized fuel lifts the needle check 248 after aselected pressure level is reached and the highly pressurized fuel isinjected through the injection spray orifices 286.

In order to end injection or control the quantity of fuel injected, theelectronic control module 454 discontinues its fuel delivery commandsignal S₁₀ to the electronic drive unit. The electronic drive unit thendiscontinues its waveform thereby electrically de-energizing thesolenoid assembly 36 of the selected unit injector 18. The absence ofthe opposing magnetic force allows the compressed poppet spring 78 toexpand causing both the armature 42 and poppet valve 38 to move back totheir first position. The poppet valve 38 passes through its secondposition where its lower seat 149 opens fluid communication between theinlet passage 158 and the piston pump chamber 190 while maintainingfluid communication between the piston pump chamber 190 and the upperannular peripheral groove 144, passage 128 and drain passage 108. Duringthis portion of the displacement of the poppet valve 38, the actuatingfluid communicated from the inlet passage 158 is depressurized and allor a portion of it is exhausted directly back to the sump 316. Duringhot engine operating conditions, the depressurized actuating fluid isused as damping fluid which can leak past the clearance C_(3a) in orderto decelerate the velocity of the poppet valve 38 as it approaches itsfirst position.

At the first position, the lower seat 149 of the poppet valve 38 seatson the annular valve seat 166 of the body 80 which blocks high pressureactuating fluid from communicating with the piston pump chamber 190.Moreover, the upper seat 146 of the poppet valve 38 is unseated from theannular seat 129 of the poppet sleeve 76 thereby communicating thepiston pump chamber 190 with the the upper annular peripheral groove144, passage 128 and drain passage 108.

Once the piston pump chamber 190 is in fluid communication with theannular peripheral groove 144, passage 128 and drain passage 108, thefluid pressure acting on the intensifier piston 88 also decreasesthereby stopping downward displacement of the intensifier piston 88 andplunger 204. The compressed plunger spring 206 then expands therebyreturning the plunger 204 and intensifier piston 88 against the seat 170of the body 80. The pressure in the expanding fuel pump chamber 260decreases which allows the compressed needle check spring 238 to movethe needle check 248 downwardly against its seat 282. The decreasedpressure in the fuel pump chamber 260 also allows the check valve 230 tounseat thereby permitting the fuel pump chamber 260 to refill with fuel.

During cold engine startup conditions, the viscosity of the actuatingfluid is relatively high if the actuating fluid is chosen to be enginelubricating oil. The presence of cold and very viscous actuating fluidin the clearances C₁, C₂ is undesirable because it can impede orcompletely restrain the motion of the armature 42 and poppet valve 38.The size of the annular clearance C_(3a) between the poppet valve 38 andthe poppet sleeve 76 is preferably chosen so that it is small enough torestrict communication of relatively cold actuating fluid from the upperannular peripheral groove 144 of the poppet valve 38 to the upper poppetvalve cavity 138 and lower armature cavity 89 during engine startup.Thus, the movable armature 42 and poppet valve 38 are free to operatewithout cold and viscous actuating fluid being present in the clearancesC₁,C₂. The effective flow restriction provided by the clearance C_(3a)(e.g., cross-sectional area and axial length) is also preferably chosenso that it is large enough to communicate relatively hot actuating fluidbetween the upper annular peripheral groove 144 and the upper poppetvalve cavity 138 and lower armature cavity 89 during normal engineoperation. This allows the movable armature 42 and poppet valve 38 tooperate with a selected amount of damping imparted by the displacementor squishing of relatively hot actuating fluid from the clearances C₁and C₂. The size of the annular clearance C_(3a) should also be selectedin conjunction with the selection of size for the clearance C₂ betweenthe armature 42 and the poppet adapter 70. Such damping helps tominimize the tendency of the poppet valve 38 to rebound off either oneof its seats 146,149 after making initial contact.

The communicating, collecting and draining means 56, in the form ofcollection grooves 60 and passages 58, helps minimize any pumping effectthat the movable armature 42 would normally impart on the actuatingfluid contained in the upper armature cavity 57. The communicating,collecting and draining means 56 and the drain passages 98 of thearmature spacer 64 permit damping fluid that has been communicated tothe upper and lower armature cavities 57,89 to drain back to the sump316 without hydraulically locking the position of the armature 42 andpoppet valve 38. The communicating, collecting and draining means 56 andthe armature spacer drain passages 98 also permit hot actuating fluid todrain from the upper and lower armature cavities 57,89 so that theactuating fluid cannot remain there, cool off, and possibly become veryviscous fluid under cold engine starting conditions.

In order to help start the engine 12 under cold engine conditions, oneor more electrical signals (for example, square pulses of electricalcurrent) having a selected amplitude, pulsewidth and period may beapplied to the actuator assembly 36 over a selected time span prior tocranking the engine 12. The selected amplitude, pulsewidth, period, andtime span are carefully chosen so as not to overheat and damage theactuator assembly 36. The pulses of current may be supplied by eitherthe electronic drive unit, engine battery, or a combination of the two.The periodic electrical signals may cause the spring-biased armature 42to reciprocate and thereby expel at least a portion of the viscousdamping fluid from the upper and lower armature cavities 57,89. Oneimportant effect is the reduction of fluid film strength in the cavity57 between the armature 42 and the stator 46. Another important effectis that the actuator assembly 36 is heated up so that it can help warmup the damping fluid that is eventually communicated to it via theclearance C_(3a) between the poppet valve 38 and the poppet sleeve 76.Each of these effects facilitates quicker response of the poppet valve38 for improved fuel injection delivery capability and timing accuracyduring engine startup.

This engine starting strategy may be further refined by detecting thetemperature of the actuating fluid in, for example, at least one of themanifolds 334,336 and implementing this starting strategy only when thetemperature falls below a selected level. Alternatively, another engineparameter which indirectly indicates the temperature of actuating fluidin the manifolds 334,336, such as engine coolant temperature, may bedetected and used for determining whether or not to implement thisstarting strategy.

In addition to or as an alternative to the above cold engine startingstrategy, such one or more electrical signals may be applied to theactuator assembly 36 over a selected time span after the engine 12 hasbeen stopped. When the engine 12 is stopped, it no longer drives thehigh pressure actuating fluid pump 332. The electrical signals cause thespring-biased armature 42 to reciprocate and thereby expel at least aportion of the hot damping fluid from the upper and lower armaturecavities 57,89 before the damping fluid cools off and becomes moreviscous. This strategy may be further modified by detecting ambient airtemperature and applying the electrical signals to the actuator assembly36 after engine 12 is stopped but only when the ambient air temperaturefalls below a selected value.

Under cold engine operating conditions, an extended fuel deliverycommand signal or logic pulse may be required in order to effect startupof a cold engine 12. The length of time required for the fuel deliverycommand is a function of actuating fluid viscosity due to variouspressure drops in the circuit. Without precisely knowing what the oilviscosity is, it is difficult to calculate or estimate the exact lengthof time required for the fuel delivery command signal under cold enginestarting conditions. If the time is underestimated, insufficient fuelinjection is effected. If the time is overestimated, excessive fuelinjection is effected which may over fuel and damage the engine.

One solution to the above problem of improving cold engine startingcapability is to provide a sensor for directly or indirectly detectingthe viscosity or temperature of the actuating fluid, generating aviscosity or temperature indicative signal which is sent to theelectronic control module 454, and using a pulse width multiplierstrategy to compensate for variations in the detected viscosity ortemperature of the actuating fluid. The electronic control module 454 isprogrammed so that at normal engine operating temperatures, the maximumfuel delivery command signal S₁₀ is limited by a selected maximumpulsewidth which is selected to improve governability of the engine 12and/or avoid excessive engine torque. Such selected maximum pulsewidthmay be insufficient to achieve cold engine starting. Therefore, theelectronic control module 454 is also programmed so that only duringengine startup, the selected maximum pulsewidth is multiplied andincreased by a factor wherein the factor is selected as a function ofthe detected viscosity or temperature of the actuating fluid. Generally,the factor increases from one to a number greater than one as thedetected viscosity of the actuating fluid increases or the detectedtemperature of the actuating fluid decreases. After the engine 12 hasstarted and the actuating fluid reaches normal engine operatingtemperature or viscosity, the selected factor becomes one.

For example, the method of starting the engine 12 may comprise the stepsof the electronic control module 454 applying at least one electricalfuel delivery command signal S₁₀ of a selected first pulsewidth to theactuator and valve assembly 28 of the unit injector 18, supplyingpressurized actuating fluid to the unit injector 18 in response to thefuel delivery command signal S₁₀ of the first pulsewidth, hydraulicallydisplacing the intensifier piston 88 of the unit injector 18 over afirst displacement to effect a first fuel injection quantity in responseto the fuel delivery command signal S₁₀ of the first pulsewidth, andapplying at least another electrical fuel delivery command signal S₁₀ ofa selected second pulsewidth to the unit injector 18 after the engine isstarted wherein the second pulsewidth is chosen to be less than thefirst pulsewidth. The method further includes the steps of supplyingpressurized actuating fluid to the unit injector 18 in response to theanother fuel delivery command signal S₁₀ of the second pulsewidth andhydraulically displacing the intensifier piston 88 of the unit injector18 over a second displacement to effect a second fuel injection quantityin response to the another fuel delivery command signal S₁₀ of thesecond pulsewidth wherein the second displacement is less than the firstdisplacement. Consequently, the second fuel injection quantity is lessthan the first fuel injection quantity. Alternatively, the electroniccontrol module 454 may apply a series of electrical fuel deliverycommand signals S₁₀ during engine startup wherein the pulsewidths of thesignals gradually decrease from one selected magnitude to anotherselected magnitude.

Another solution to the above problem is to selectively vary thepressure of the actuating fluid supplied to the unit injectors 18. Thepressure is varied by the electronic control module 454 varying theactuating fluid manifold pressure command signal S₉ to the primarypressure regulator 368. For example, the method of starting the engine12 may comprise the steps of the electronic control module 454 applyingan electrical fuel delivery command signal S₁₀ to the unit injector 18,supplying actuating fluid of a selected first pressure to the unitinjector 18 in response to application of the fuel delivery commandsignal S₁₀, hydraulically displacing the intensifier piston 88 of theunit injector 18 over a first displacement to effect fuel injection, andapplying another electrical fuel delivery command signal S₁₀ to the unitinjector 18 after the engine is started. The method further includes thesteps of supplying actuating fluid of a selected second pressure to theunit injector 18 in response to application of the another fuel deliverycommand signal S₁₀ wherein the second pressure is chosen to be less thanthe first pressure, and hydraulically displacing the intensifier piston88 of the unit injector 18 over a second displacement to effect fuelinjection wherein the second displacement is less than the firstdisplacement. Alternatively, the electronic control module 454 may varythe actuating fluid supply pressure during engine startup such that thepressure gradually decreases from one selected magnitude to anotherselected magnitude.

Another solution to the above problem is to not only selectively varythe pressure but also vary the pulsewidths of the fuel delivery commandsignals S₁₀. In the above examples, the magnitudes of the actuatingfluid pressure and/or the fuel delivery command pulsewidths may beselected as a function of the viscosity or temperature of the actuatingfluid or another parameter which indirectly indicates such viscosity ortemperature.

Another solution to the above problem is to set the clearance C₄,between the barrel seat 219 and the second stop 196 of the intensifierpiston 88, to a selected axial length which corresponds to the maximumallowable effective stroke of the intensifier piston 88 and plunger 204.For example, the clearance C₄ may be chosen to be about 3.5 millimetersor 0.136 inches. The unit injector 18 is thus mechanically limited toinjecting a selected maximum amount of fuel under any conditions,including cold engine operation or startup. During cold engineoperation, the electronic control module 454 delivers a fuel deliverycommand signal S₁₀ having a relatively long time duration or pulsewidthwithout regard to actual oil viscosity but which is sufficient to effectthe maximum displacement of the intensifier piston 88. The magnitude ofthe clearance C₄ is chosen so that sufficient fuel is injected forensuring adequate starting and acceleration of the engine 12 but notmore than would cause overfueling damage to the engine 12 and/ordrivetrain. The magnitude of the clearance C₄ is also chosen so that itis smaller than the corresponding clearance between the free end of theplunger 204 and the stop member 232. Thus, if the fuel supplying means22 runs out of fuel during engine operation, the intensifier piston 88contacts its seat 219 first and thereby prevents the plunger 204 fromstriking the stop member 232 and causing possible distortion of theplunger 204 and/or the barrel 198. After engine startup is achieved, theelectronic control module 454 is programmed to reduce the pulsewidth ofthe fuel delivery command signal S₁₀ to a time duration sufficient tomaintain a desired engine speed.

The following is a summary of the main advantages of the HEUI fuelinjection system 10 over a mechanically-actuated fuel injection system.First, the HEUI fuel injection system 10 eliminates various conventionalmechanical components, such as the cam and rocker arm mechanism, used toactuate the fuel pumping plunger. Such elimination of components helpsreduce cost and improve reliability and packaging of the engine 12. Dueto the above advantages, the HEUI fuel injection system 10 is alsoattractive for retrofitting to existing conventional engines which donot yet have electronically-controlled fuel injection systems. Second,the fuel injection pressure of the HEUI fuel injection system 10 can beselected or even varied to optimal values independent of the speed ofthe engine 12. For example, during engine startup the magnitude of theinjection pressure may be increased to a selected value in order toimprove startability of the engine 12. At low engine load and low enginespeed conditions, the magnitude of the injection pressure may be loweredto a selected value in order to reduce atomization of the injected fuelso that the fuel burns slower and causes quieter operation of the engine12. At high engine load and low engine speed conditions, the magnitudeof the injection pressure may be raised to a selected value in order toreduce the amount of particulates emitted by the engine 12. At partialload conditions, the magnitude of the injection pressure may be loweredto a selected value in order to reduce fuel consumption by the engine12. In each of the above examples, the pulsewidth of the fuel deliverycommand signal S₁₀ may also be varied for optimum engine performanceand/or minimal emissions. The closed-loop feedback circuit helps ensurethat a desired pressure setting is achieved and maintained for as longas desired.

Other aspects, objects, and advantages of this invention can be obtainedfrom a study of the drawings, the disclosure, and the appended claims.

I claim:
 1. An actuator and valve assembly adapted for anelectronically-controlled injector comprising:anelectrically-energizable actuator assembly including a movable member;damping means for fluid damping the motion of the movable member; avalve connected to the movable member and adapted to selectivelycommunicate damping fluid to the damping means; and restriction meansfor restricting the communication of damping fluid to the damping meansin direct proportion to the viscosity of the damping fluid.
 2. Theactuator and valve assembly of claim 1 wherein said restriction means ispositioned in the damping fluid flowpath between the valve and thedamping means.
 3. The actuator and valve assembly of claim 1 whereinsaid restriction means includes a sleeve defining a sleeve bore, saidvalve having an end portion positioned in the sleeve bore according to apredetermined diametrical clearance, said diametrical clearance having apredetermined length and cross-sectional area which effectivelyrestricts the communication of damping fluid to the damping means indirect proportion to the viscosity of the damping fluid.
 4. The actuatorand valve assembly of claim 1 wherein said movable member is anarmature.
 5. The actuator and valve assembly of claim 1 wherein saidinjector is a unit injector.
 6. An actuator and valve assembly adaptedfor an electronically-controlled injector comprising:a first memberdefining a first member bore; an electrically-energizable actuatorassembly including a movable second member defining a cavity; a valveconnected to the movable second member and adapted to selectivelycommunicate damping fluid to the injector, said valve having an endportion positioned in the first member bore according to a predetermineddiametrical clearance; and means for communicating damping fluid withrespect to the cavity of the actuator assembly, said diametricalclearance having a predetermined length and diameter which effectivelycontrols communication of damping fluid to the cavity according to theviscosity of the damping fluid.
 7. An actuator and valve assemblyadapted for a hydraulically-actuated electronically-controlled injectorcomprising:a first member defining a first member bore; anelectrically-energizable actuator assembly including a movable secondmember defining a cavity; a valve connected to the movable second memberand adapted to selectively communicate hydraulically actuating fluid tothe injector, said valve having an end portion positioned in the firstmember bore according to a predetermined diametrical clearance; andmeans for communicating damping fluid with respect to the cavity of theactuator assembly, said diametrical clearance having a predeterminedlength and diameter which effectively controls communication of dampingfluid to the cavity according to the viscosity of the damping fluid. 8.An actuator and valve assembly adapted for a hydraulically-actuatedelectronically-controlled injector comprising:a sleeve defining a sleevebore; an electrically-energizable actuator assembly including a movablemember defining first and second cavities; a valve connected to themovable member and adapted to selectively communicate hydraulicallyactuating fluid to the injector, said valve having an end portionpositioned in the sleeve bore according to a predetermined diametricalclearance; and means for communicating, collecting and draining dampingfluid with respect to at least one of the cavities of the actuatorassembly, said diametrical clearance having a predetermined length anddiameter which effectively controls communication of damping fluid tothe at least one of the cavities according to the viscosity of thedamping fluid.
 9. An actuator and valve assembly adapted for ahydraulically-actuated electronically-controlled injector comprising:anelectrically-energizable solenoid assembly including a fixed stator anda movable armature, said armature having first and second surfacesdefining first and second cavities, respectively, said first surface ofthe armature facing the stator; a valve connected to the armature, saidvalve adapted to selectively communicate hydraulically actuating fluidto the injector; and means for communicating, collecting and drainingdamping fluid with respect to at least one of the cavities of thesolenoid assembly, said means including a passage defined in thearmature and extending between the first and second surfaces, said meansfurther including a collection groove formed in and extending across oneof the armature first surface and the stator, said collection groovecommunicating with the passage of the armature, said passage of thearmature adapted to communicate with a drain passage.
 10. The actuatorand valve assembly of claim 9 wherein said valve has a first end portiondefining a first valve cavity, a second end portion defining a secondvalve cavity, and an intermediate portion positioned between the valvecavities, said intermediate portion defining a restricted passage whichcommunicates between the valve cavities.